The present disclosure relates generally to semiconductor fabrication, and more particularly, to semiconductor fabrication process control.
As performance requirements and throughput demands increase, semiconductor fabrication process control has become even more crucial. However, as process geometries decrease, such as from 65 to 45 nanometer and beyond, it may be challenging to keep process variations at acceptable levels. As such, the processes may suffer from losses in tool productivity, increased operator interaction, yield loss, and higher rework rates, all possibly leading to higher costs. Advanced Process Control (APC), which may consist of models and feedback systems among other process control techniques, has been widely used to help alleviate some of the variations. However sufficient APC methods are lacking, especially for controlling and tuning parameters that are affected by multiple process steps. In some applications, noise signals from various aspects of semiconductor fabrication can influence and disturb the APC design and implementation. The noise signals may come from previous stages of fabrication, present operating conditions, and APC actions, themselves. Consequently, although existing APC techniques have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects.